Variables

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# 4. Variables

Variables are named cells stored in the computer memory that can hold any single Perl value. One can change the value that a variable holds, and one can later retrieve the last value assigned as many times as wanted.

Variables in Perl start with a dollar sign (`$`) and proceed with any number of letters, digits and underscores (`_`) as long as the first letter after the dollar is a letter or underscore.

To retrieve the value of a variable one simply places the variable name (again including the dollar sign) inside an expression.

To assign value to a variable, one places the full variable name (including the dollar sign) in front of an equal sign (`=`) and places the value to the right of the equal sign. This form is considered a statement and should be followed by a semicolon. The value assigned may be an experssion that may contain other variables (including the assigned variable itself!).

An example will illustrate it:

    $myvar = 17;
    $a = 2;
    print $myvar, " * ", $a, " = " , ($myvar*$a), "\n";
    $a = 10;
    print $myvar, " * ", $a, " = " , ($myvar*$a), "\n";
    $a = 75;
    print $myvar, " * ", $a, " = " , ($myvar*$a), "\n";
    $a = 24;
    print $myvar, " * ", $a, " = " , ($myvar*$a), "\n";

The output of this program is:

    17 * 2 = 34
    17 * 10 = 170
    17 * 75 = 1275
    17 * 24 = 408

Several things can be noticed:

1. The value of `$a` changes throughout the program. It's perfectly fine, and usually even necessary to modify the value of a variable.
2. By using `$myvar` we can ensure, that assuming we wish to change its value, we will only have to change it in one place, not in every place it appears.

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